As the integration density of integrated circuit memory devices increases, there are typically decreases in, for example, the area of memory cells in the device. Decreasing the area of memory cells in the device may reduce the capacitance of capacitors in such devices. To increase the effective area of a three-dimensional capacitor on a substrate a thin dielectric layer may be interposed between upper and lower electrodes of a capacitor. The dielectric layer preferably comprises a material having high dielectric constant. However, manufacturing processes associated with forming such capacitors may be complex and relatively expensive. In addition, Fowler-Nordheim currents may cause decreased reliability of resultant devices if the thickness of the dielectric layer is smaller than, for example, 100 A.
These problems have made the use of high dielectric constant ferroelectric substances an attractive choice for the dielectric layer of capacitors in integrated circuit memory devices. Like ferromagnetic substances, ferroelectric substances have a hysteresis characteristic in which a remnant polarization value changes under a given electric field. Thus, ferroelectric substances can have a remnant polarization (Pr) even in the absence of an external electric field. One important parameter in determining the operating voltage of a device can be referred to as a coercive electric field. The coercive electric field is present when the external electric field causes the value of the remnant polarization (Pr) to be 0. The remnant polarization (Pr) makes reading and writing possible in, for example, ferroelectric RAM (FRAM) devices.
However, when the dielectric layer of the capacitor comprises a ferroelectric material, the dielectric characteristic of the dielectric layer can be degraded during manufacturing of integrated circuit memory devices. For example, after the capacitor is be formed, an interlayer dielectric (ILD) process, an intermetal dielectric (IMD) process and a passivation process may be performed. In performing these processes, chemical vapor deposition (CVD) and/or plasma enhanced CVD (PE-CVD) deposition processes can be used in which hydrogen gas and/or silane (SiH4) gases are used as a carrier gas. However, when carrier gases such as these are used, the gas can directly react with oxygen present in the ferroelectric material, such as Pb(ZrTi)O3 and/or SrBi2Ta2O9, to yield water (H2O). As a result, the ferroelectric material may lack oxygen which can degrade electrical characteristics of the ferroelectric material.
To solve this problem, a method of encapsulating a capacitor with a single insulation layer has been used. For example, U.S. Pat. No. 5,822,175 discloses a method of encapsulating a capacitor with a silicon oxide layer, a doped silicon nitride layer and a silicon nitride layer to reduce degradation of the dielectric layer. To enhance the insulation properties of the dielectric layer, an annealing process can be performed in an oxygen atmosphere at a temperature of 600–800° C. Unfortunately, hydrogen can be generated when an encapsulating layer is formed. This hydrogen may diffuse into the dielectric layer. Moreover, the diffusion of hydrogen can be accelerated during the succeeding annealing process.